DESCRIPTION (Investigator's Abstract): Regulation of neurotransmitter synthesis is crucial to the development and normal functioning of neurons. Much progress has been made in identifying factors which regulate catecholamine (CA) synthesis in the peripheral nervous system. In contrast, very little is known about this process in brain. Recent experiments (Iacovitti et al., 1989) have now demonstrated that synthesis of tyrosine hydroxylase (TH), the rate limiting enzyme in CA synthesis, is profoundly increased in certain embryonic brain neurons when they are exposed to a muscle cell extract in tissue culture. The induction of TH is dose dependent and results from a diffusible molecule(s) termed the Muscle-Derived Differentiation Factor (MDF). The identify of MDF remains unknown. In an exhaustive survey, its effects could not be reproduced by other factors known to regulate TH. MDF dramatically induces TH in catecholamine neurons (substantia nigra) as well as in neurons that do not normally express a CA phenotype (cerebral cortex and striatum). MDF exerts its influence at the level of gene expression, up-regulating TH mRNA transcription at least 10-fold. As such, MDF is the first factor described which regulates the TH gene in brain neurons. The proposed project aims to purify and identify MDF. Refinement of the MDF assay, based upon the immunocytochemical detection of TH, has now made purification an obtainable goal. Preliminary experiments indicate that MDF is a fairly stable macromolecule that will be amenable to a variety of fractionation methods. Concurrent with purification, experiments are proposed which can be carried out with partially pure MDF. The signal transduction pathway by which the TH gene is regulated will be investigated by artificially inducing second messenger systems in an attempt to reproduce the effects of MDF. Finally, MDF's effects will be studied in situ in animal models of disease involving compromise of brain catecholamine systems. We will assess anatomical, biochemical and behavioral recovery in lesioned/grafted brain following MDF treatment. The long range goal of this work is to elucidate the mechanisms controlling the expression of catecholamines in the brain. These studies are of clinical relevance since a number of neurological and psychiatric disorders are associated with imbalances in brain CA's; most notable, is Parkinson's Disease, but also Alzheimers Disease, clinical depression and schizophrenia.